Fluid density digital computer

ABSTRACT

Apparatus for producing a digital output from a storage register directly proportional to fluid density. A count down counter is preset to

United States Patent November FLUID DENSITY DIGITAL COMPUTER Primary Examiner--Thomas A. Robinson Assistant Examiner-Joseph M. Thesz, Jr.

[75] Inventor: Mliton Niwember Haclend Attorney-C. Cornell Remsen, Jr. et al. and A. Donald Heights, Calif. Stolzy [73] Assignee: International Telephone and Telegraph Corporation, New York, [57] ABSTRACT Apparatus for producing a digital output from a stor- [22] Filed: Dec. 27, 1972 a e register directly proportional to fluid density. A

g 1 [211 App] No 318 836 count down counter is preset to STT /R 521 U.S. c1 235/92 MT, 235/1515, 73/32, where 5, o T and R are constants Constants R and S 235/92 Cp 235/92 R may be found empirically from a simple vibration den- 51 Int. Cl. G06f 15/56 Siwmeter test Constant T is more or less arbitrary- [58] Field of Search 235/92 MT, 92 CP, The Pulse Output of the densitometer is then p y 235 15 3 15 35; 73 32 to cause the counter to count down for periodic time invariant gating intervals. The number in the counter 5 References Cited at the end of each such interval is then entered in the UNITED STATES PATENTS storage register, this number being directly proportional to density. The system of the disclosure can be 3,655,956 4/1970 Ley 235/92 MT employed to reduce analog computer error to an insig nificant magnitude.

13 Claims, 7 Drawing Figures ew/TcH MAT/27X /A 6;7T/A/6 i c/Rcu/ T 2/ 0,2 GATE MATRIX l "75 a l LOG/C STORAGE i c/Rcu/rl REG/S7752. i I 4 24M; xmr. g GQT/A/G /Z4 ooclum'o/a c/ecu/ T f 3 //VD/CQTOEIP 2? STORAGE EGG/575R 52 Lee/c C/QCU/T -55 ONE I PULSE Pmmeunnm ms SHEET 0F 5 mwm , 1 FLUID DENSITY DIGITAL COMPUTER BACKGROUND OF THE INVENTION This invention relates to apparatus for producing an output directly proportional to the density of a fluid, and'more particularly, to a digital computer for use with fluid densitometer components.

In the past it has been the practice to compute fluid density from the output of vibration densitometer ap' paratus by the use of analog computers. There are, therefore, added inaccuracies because analog computers introduce certain finite errors which cannotbe eliminated.

SUMMARY OF THE INVENTION In accordance with the system of the present inven tion, the above-described and other disadvantages of the prior art are overcome by entering a predetermined number in the main register of a count down counter and using the densitometer output pulses to cause the counter to count down. The number remaining in the main registerafter a fixed counting interval is then proportional to the fluid density.

The above-described and other advantages of the present invention will be better understood from the following detailed description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which are to be regarded as merely illustrative:

FIG. I is a block diagram of one embodiment of the present invention;

FIG. 2 is a schematic diagram of several of the blocks shown in FIG. 1;

FIG. 3 is a truth table for a count down counter;

FIG. 4 is a detailed block diagram of a count down counter;

FIG. 5 is a truth table for a storage register shown in FIG. 1;

FIG. 6 is a detailed block diagram of a storage register and logic circuit shown in FIG. I; and

FIG. 7 is a graph of a groupof waveforms characteristic of the operation of the invention shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT A pulse source 10 is shown in FIG. 1 connected to a gate 11. Pulse source 10 may, if desired, be identical to all structures shown in FIG. 7 of U. S. Pat. No. 3,677,067, with the exception of linearization circuit 109 and indicator 110. The output of a tracking filter 91 also illustrated in this patent may then be connected as an input to gate 11 herein.

The output of pulse source 10 herein has a pulse repetition frequency f. The vibration densitometer probe disclosed in U. S. Pat. No. 3,677,067 is immersed in a fluid. The density d of this fluid over a reasonable range can then be determined from the equation The terms R and S are generally positive constants which can be determined empirically from an instrument by measuring f twice with the probe in two different respective fluids of known densities. (See the said patent).

Something about certain structures disclosed herein is discussed in the material immediately following. The importance of some of this discussion may be apparent only from subsequent explanations.

A main storage register D is illustrated in FIG. 1. As will be described, a predetermined number V is entered in storage register D periodically. This number is V STT /R where T is the time width of pulses on an output lead 16 of a logic circuit 15 shown in FIG. 1, and T is an arbitrary constant. For the apparatus shown in FIG. 1, T may be equal to unity.

A logic circuit is provided at 13. Logic circuit 13 has an input 14 which receives pulses when gate 11 is open, at a rate in the general case Tf. However, gate 1 1 does not modify f at the output of source 10 in FIG. 1. Thus, in the specific case of FIG. 1, Tf f because T= 1.

Logic circuit 15 impresses gating pulses on gate 11 over lead 16. Each of these gating pulses have the same time width. This time width is large in comparison to the reciprocal of Tf.

Logic circuit 15 also has output leads l7 and 18. The pulses on output leads 16, 17 and 18 may be further identified herein as pulses pg, pr and pc, respectively, having pulse repetition frequencies fg, fr and fc, respectively, where fg fr =fc.

In FIG. 1, the said predetermined number V is periodically entered in storage register D. The magnitude of the predetermined number may be selected or changed by operating certain switches, to be described, which are located in a switch matrix A. The switches in matrix A are either connected from a positive potential V1 or ground. The outputs of the switches are sampled and impressed upon storage register D periodically. A sampling gate is, thus, impressed upon a gating circuit B over a lead 21 for this purpose.

Gating circuit B is connected from matrix A to an OR gate matrix C. The output of OR gate matrix C is then impressed upon storage register D.

Once the said predetermined number V has been entered into storage register D, logic circuit 13 then controls the register D to count down. The output of logic circuit 13 is, thus, impressed upon storage register D through OR gate matrix C. Logic circuit 13 receives pulses to count at input 14. Logic circuit 13 receives other inputs from storage register D.

From the foregoing, it will be appreciated that matrix C with logic circuit 13 and storage register D form a count down counter. This counter may be entirely conventional, if desired. The count down counter is indicated at 23. I

The output of storage register D is also sampled periodically by a gating circuit 24 which may be of the same type as gating circuit B. Gating circuit 24 receives pulses to cause it to sample the output of register D over a lead 25. The output of gating circuit 24 is impressed upon a storage register 26. The output of the storage register 26 is impressed upon an indicator 27.

If desired, indicator 27 may be binary coded decimal.

All of the structures D, 13, A, B, C, 24, 26 and 27 may be entirely conventional by themselves, although the combination thereof is new.

Alternatively, indicator 27 may simply be a row of lamps each connected from the 1 output of each of the flip-flops in storage register 26.

Pulses are supplied to leads 21 and 25, and to input 14 responsive to the outputs of logic circuit 15. Logic circuit 15 operates from a 2 megahertz crystal oscillator 28. A squarer 29, a divide-by-one thousand divider 30, and a divide-by-one thousand divider 31 are connected in succession in that order from oscillator 28 to logic circuit 15. Logic circuit 15 and a storage register 32 connected therewith operate, more or less, as a counter. Logic circuit output lead 18 is connected to lead through a delay 33. Logic circuit output lead 17 is connected to lead 21. Logic circuit output lead 16 is connected to the gate 11. The output of pulse source 10 is also connected to gate 11. The output of gate 11 is connected to input 14 through a one-shot multivibrator 34.

As shown in FIG. 2, the purpose of the switch matrix A is to set, periodically, the flip-flops in storage register D to selected states. Switch matrix A includes doublepole, double-throw switches Al, A2, A3 An.

Gating circuit B includes swiches BIA, B2A, B3A BnA connected respectively from the upper poles of switches A. Gating circuit B also includes switches B1B, B2B, B3B BnB connected respectively from the lower poles of the switches A. Lead 21 is connected to each of the switches B to operate the same. The switches B may be entirely conventional electronic switches, if desired.

OR gate matrix C includes OR gates CIA, C2A, C3A CnA having inputs ClAl, C2Al, C3A1 CnAl, respectively. OR gates ClA, C2A, C3A CnA also have input leads C1A2, C2A2, C3A2 CnA2, respectively.

OR gate matrix C also includes OR gates ClB, C2B, C3B CnB which have inputs CIBI, C2B1, C3B1 CnBl, respectively. The OR gates ClB, C2B, C3B CnB also have inputs ClB2, C282, C382 CnB2, respectively. The OR gate inputs C1Al, C2A1, C3Al CnAl are connected respectively from switches BIA, 82A, 83A BnA. The OR gate inputs ClBl, C2BI, C3Bl CnBl are connected respectively from switches B1B, B2B, B3B BnB.

The OR gate inputs CIA2, C2A2, C3A2 CnA2, and the OR gate inputs C1B2, C2B2, C3B2 CnB2 are respectively connected from corresponding outputs of logic circuit 13.

Storage register D includes flip-flops D1, D2, D3 Dn. Flip-flops D1, D2, D3 Dn have set 1 inputs DlA, D2A, D3A DnA respectively connected from the outputs of OR gates CIA, C2A, C3A CnA, respectively. Flip-flops D1, D2, D3 Dn also have set 0 inputs DlB, D2B, D3B DnB respectively connected from the outputs of OR gates C18, C28, C38 CnB, respectively.

As will be noted in FIG. 2, the outputs of flip-flops D are connected both to logic circuit 13 and to gating circuit 24.

A truth table for a typical count down counter is shown in FIG. 3. A counter 35 therefor is shown in FIG. 4. The counter of FIG. 4 has a storage register 36 including only three flip-flops X, Y and Z. With the logic shown, the counter is adapted to count down only from 1, 2, 3, 4 or 5.

In FIG. 4, counter 35 includes AND gates 37, 38, 39, 40 and 41. Counter 35 also includes OR gates 42, 43, 44, and 46. In FIG. 4, counter 35 also includes OR gates 47, 48, 49, 50, 51 and 52. OR gates 4752 receive inputs over leads 53-58 from a reset input. That is, for

the counter to count down, there must first be a number entered over the leads 53-58. That is the purpose of the OR gates 4752. That is, the OR gates 4752 not only permit the control of the flip-flops X, Y and Z, according to the count down logic, the OR gates 4752 also permit the entry of a number in the register 36. In general, the reset input on leads 53-58 will be supplied at a time different from the time that clock pulses are supplied to each of the AND gates 37-41 over a lead 59. Thus, the OR gates 47-52 perform precisely the same function as OR gates C in FIG. 2.

As stated previously, in general, register 32 and logic circuit 15, shown in FIG. 1, form a counter. The logic of this counter is illustrated in FIG. 5.

Register 32 and logic circuit 15 are again shown in FIG. 6. As shown in FIG. 6, register 32 includes only two flip-flops M and N. Logic circuit 15 has four AND gates 60, 61, 62 and 63. Logic circuit 15 has four OR gates 64, 65, 66 and 67. Logic circuit 15 also has four AND gates 68, 69, 70 and 71.

If the input to logic circuit 15 from divider 31 is considered to be a clock pulse Cp, the logic of the gates in logic circuit 15 may be expressed as follows, the clock pulse input to logic circuit 15 from divider 31 being applied over a lead 74. The logic of gate is MN. The logic of gate 61 is MN. The logic of gate 62 is MN. The logic of gate 63 is MN. The logic of gate 64 is MN MN. The logic of gate 65 is MN MN. The logic of gate 66 is MN+ MN. The logic of gate 67 is MN MN.

The logic of gate 68 is Cp (MN MN). The logic of gate 69 is Cp (MN MN). The logic of gate 70 is Cp (MN+ MN). The logic of gate 71 is Cp (MN MN).

A differentiator 72 and a one-shot 72' are connected from AND gate 60 to delay 33. A differentiator 73 and a one-shot 73 are connected from AND gate 60 to lead 17.

The output of divider 31 may be as illustrated at (a) and (e) in FIG. 7.

The mark-to-space ratio of the waveform of (a) in FIG. 7 may be unity, if desired. However, this is by no means critical. The period of the waveform of (a) in FIG. 7 may be one-half second, if desired. However, again, this period is not critical.

The waveform appearing on the output lead 16 of logic circuit 15 shown in FIG. 1 is illustrated at (b) in FIG. 7. This waveform appears on the output lead in FIG. 6 labeled 74.

Pulse source 10 in FIG. 1 may produce output pulses as indicated at (c) in FIG. 7. However, the pulse repetition frequency of the pulses (c) in FIG. 7 has been greatly reduced for clarity. Actually, the pulse repetition frequency of the output pulses of source 10 may vary about 4.0 kilohertz, if desired.

The pulses appearing on the output lead labeled to delay 33 in FIG. 6 are illustrated at (f) in FIG. 7.

The output of delay 33 is indicated at (g) in FIG. 7. The pulses at (g) in FIG. 7 may, thus, be delayed relative to the pulses (f) in FIG. 7 by a time Q, if desired. The pulses appearing upon the output lead 17 of logic circuit 15 in FIGS. 1 and 6 are illustrated at (h) in FIG. 7.

Delay 33, in some cases, may be eliminated entirely. Delay 33 may be any conventional delay, if desired.

The pulses (g) and (h) in FIG. 7 may be much narrower than shown, as desired. Further, in some cases, the pulses of (g) and (h) in FIG. 7 may occur simultaneously. Although it is not absolutely required, in some cases, preferably the leading edge of the pulses (g) in FIG. 7 do not occur prior to the trailing edges of the I pulses (b) in FIG. 7, the leading edges of the pulses (h) do not occur prior to the trailing edges of pulses (g), and the leading edges of the pulses (b) do not occur prior to the trailing edges of the pulses (h).

From the foregoing, it will be appreciated that the outputs of logic circuit 13 are disconnected from OR gate matrix C except during receipt of a pulse from the output of one-shot multivibrator 34 in FIG. 1. For example, in FIG. 4, gates 37-41 produce no output except during receipt .of pulses over lead 59.

The word indicate as used herein in any of its grammatical forms hereby is defined to include, but not be limited to, an indication which either is visual or is not visual. Moreover, the output of storage register 26 may be employed for process control without the use of any indicator such as indicator 27.

The phrase utilization means as used herein is hereby defined to include an indicator, a process controller or otherwise.

Although a symbol has been used consistently in the drawings to represent OR gates, it is to be understood that this symbol includes, but is not limited to, a wire OR gate. Thus, one or more or all of the symbols employed herein to represent an OR gate may or may not be a wire OR gate, as desired.

The phrase OR gate as used herein is hereby defined to include a NOR gate with or without an inverter, as necessary or desirable.

What is claimed is:

l. A digital control system comprising: densitometer apparatus for producing output pulses at a pulse repetition frequency f approximately proportional to the density d of a fluid such that where R and S are constants; a main storage register; reset means to enter a predetermined number into said main register periodically, said predetermined number being equal to V, where V STT /R T is the time width of a pulse pg, and T is a constant; a gate; synchronization means, logic means connected to and from said main register and from said gate to cause the count stored in said main register to be reduced by one upon receipt thereby of each output pulse of said gate; an output storage register; a gating circuit connected from said synchronization means and said main storage register to said output storage register, said gate being connected from said densitometer apparatus, said synchronization means being constructed to impress pulses pg on said gate to cause said gate to pass densitometer apparatus pulses to said logic means at a rate equal to Tf, said synchronization means holding said gate open periodically for periods large in comparison to the reciprocal of Tf, said synchronization means impressing a pulse pr periodically on said reset means to cause reset means to enter said predetermined number in said main register at a time which precedes the first output pulse of said gate after it is opened, said synchronization means being connected to said gating circuit to supply a pulse pc thereto to cause the number stored in said main register to be transferred into said output storage register after said gate is closed; and utilization means connected from said output storage register.

2. The invention as defined in claim 1, wherein said synchronization means generates said pulses pg, pr and pc in synchronism.

3. The invention as defined in claim 2, wherein said pulses pg, pr and pc have pulse repetition frequencies fg, fr and fc, respectively, where fg fr =fc, all of said pulses, pg, pr and pc occurring during mutually exclusive intervals of time, each pulse immediately succeeding a pulse pr being a pulse pg, each pulse immediately succeeding a pulse pg being a pulse pc.

4. The invention as defined in claim 3, wherein the pulse width of each of said pulses pg is invariant with time.

5. The invention as defined in claim 4, wherein said predetermined number is invariant with time.

6. The invention as defined in claim 5, wherein said reset means is manually adjustable to change said predetermined number.

7. The invention as defined in claim 6, wherein first and second sets of OR gates are provided, said first set of OR gates including OR gates ClA, C2A, C3A CnA, said second set of OR gates including OR gates ClB, C2B, C3B CnB, said main storage register having first and second sets of inputs, said first set of main register inputs being DlA, D2A, D3A DnA, said second set of main register inputs being D18, D28, D38 DnB, said OR gates CIA, C2A, C3A CnA and C18, C2B, C3B CnB being connected to corresponding respective main register inputs DlA, D2A, D3A DnA and D18, D2B, D3B DnB, said reset means having a first set of output devices BlA, B2A, B3A BnA, said reset means also having a second set of output devices B13, B28, B3B BnB, said OR gates CIA, C2A, C3A CnA and ClB, C2B, C3B CnB having first inputs ClAl, C2A1, C3A1 CnAl and C181, C2Bl, C381 CnBl, respectively, said OR gates ClA, C2A, C3A CnA and ClB, C28, C33 CnB also having second inputs C1A2, C2A2, C3A2 CnA2 and ClB2, C2B2, C3B2 CnB2, re spectively, said output devices BIA, B2A, B3A BnA being connected to said first inputs ClAl, C2A1, C3A1 CnAl, respectively, said logic circuit having corresponding respective different outputs connected to said OR gate second inputs.

8. The invention as defined in claim 7, wherein said utilization means includes means to indicate the magnitude of the number stored in said storage register.

9. The invention as defined in claim 2, wherein said first and second sets of OR gates are provided, said firstset of OR gates including OR gates CIA, C2A, C3A CnA, said second set of OR gates including OR gates ClB, C2B, C3B CnB, said main storage register having first and second sets of inputs, said first set of main register inputs being DlA, D2A, D3A DnA, said second set of main register inputs being DlB, D2B, D3B DnB, said OR gates ClA, C2A, C3A CnA and C18, C2B, C3B CnB being connected to corresponding respective main register inputs DlA, D2A, D3A DnA and D18, D2B, D3B DnB, said reset means having a first set of output devices BIA, B2A,

B3A BnA, said reset means also having a second set of output devices 818, B2B, B3B BnB, said OR gates CIA, C2A, C3A CnA and C18, C28, C38 CnB having first inputs ClAl, C2A1, C3A1 CnAl and C131, C231, C3Bl CnBl, respectively,

said OR gates CIA C2A, C3A CnA and CIB, C2B, C3B CnB also having second inputs C1A2, C2A2, C3A2 CnA2 and CIB2, C2B2, C3B2 CnB2, respectively, said output devices BIA, B2A, BSA BnA being connected to said first inputs CIAI, C2AI, C3AI CnAI, respectively, said logic circuit having corresponding respective different outputs connected to said OR gate second inputs.

10. The invention as defined in claim 3, wheein first and second sets of OR gates are provided, said first set of OR gates including OR gates CIA, C2A, C3A CnA, said second set of OR gates including OR gates CIB, CZB, C3B CnB, said main storage register having first and second sets of inputs, said first set of main register inputs being DIA, D2A, D3A DnA, said second set of mainregister inputs being D18, D28, D38 DnB, said OR gates CIA, C2A, C3A .CnA and CIB, C2B, C3B CnB being connected to corresponding respective main register inputs DIA, D2A, D3A DnA and DIB, D28, D38 DnB, said reset means having a first set of output devices BIA, B2A, B3A BnA, said reset means also having a second set of output devices BIB, B28, B38 BnB, said OR gates CIA, C2A, C3A CnA and CIB, C28, C38 CnB having first inputs CIAI, C2AI, C3AI CnAI and CIBI, C281, C381 CnBI, respectively, said OR gates CIA, C2A, C3A. CnA and CIB, C28, C38 CnB also having second inputs C1A2, C2A2, C3A2 CnA2 and CIB2, C2B2, C3B2 CnB2, respectively, said output devices BIA, 82A, 83A BnA being connected to said first inputs CIAI, C2AI, C3AI CnAl, respectively, said logic circuit having corresponding respective different outputs connected to said OR gate second inputs.

II. The invention as defined in claim 4, wherein first and second sets of OR gates are provided, said first set of OR gates including OR gates CIA, C2A, C3A CnA, said second set of OR gates including OR gates CIB, C28, C38 CnB, said main storage register having first and second sets of inputs, said first set of main register inputs being DIA, D2A, D3A DnA, said second set of main register inputs being DIB, D2B, D3B DnB, said OR gates CIA, C2A, C3A CnA and CIB, C2B, C3B .CnB being connected to corresponding respective main register inputs DIA, D2A, D3A DnA and DIB, DZB, D3B DnB, said reset means having a first set of output devices BIA, B2A, 83A BnA, said reset means also having a second set of output devices BIB, B2B, 838 BnB, said OR gates CIA, CZA, C3A CnA and CIB, C28, C38 l CnB having first inputs CIAI, C2AI, C3AI CnAI and CIBI, C281, C381 CnBI, respectively, said OR gates CIA, C2A, C3A CnA and CIB, C28, C38 CnB also having second inputs CIA2, C2A2, C3A2 CnA2 and CIB2, C2B2, C382 CnB2, respectively, said output devices BIA, B2A, B3A BnA being connected to said first inputs CIAI, C2AI,

C3A1 CnAl, respectively, said logic circuit having corresponding respective different outputs connected to said OR gate second inputs.

12. The invention as defined in claim 5, wherein first and second sets of OR gates are provided, said first set of OR gates including OR gates CIA, C2A, C3A CnA, said second set of OR gates including OR gates CIB, C2B, C3B CnB, said main storage register having first and second sets of inputs, said first set of main register inputs being DIA, D2A, D3A DnA, said second set of main register inputs being DIB, D2B, D3B DnB, said OR gates CIA, C2A, C3A CnA and CIB, C2B, C3B CnB being connected to corresponding respective main register inputs DIA, D2A, D3A DnA and DIB, D2B, D3B DnB, said reset means having a first set of output devices BIA, 82A, 83A BnA, said reset means also having a second set of output devices BIB, B2B, B3B BnB, said OR gates CIA, C2A, C3A CnA and CIB, C28, C38 CnB having first inputs CIAI, C2AI, C3AI CnAI and CIBI, CZBI, C3BI CnBl, respectively, said OR gates CIA, C2A, C3A .CnA and CIB, C28, C38 CnB also having second inputs C1A2 C2A2, C3A2 CnA2 and CIB2, C2B2, C382 CnB2, respectively, said output devices BIA, 82A, 83A BnA being connected to said first inputs CIAI, C2AI, C3A1 CnAI, respectively, said logic circuit having corresponding respective different outputs connected to said OR gate second inputs.

13. The invention as defined in claim I, wherein first and second sets of OR gates are provided, said first set of OR gates including OR gates CIA, CZA, C3A CnA, said second set of OR gates including OR gates CIB, C2B, C3B CnB, said main storage register having first and second sets of inputs, said first set of main register inputs being DIA, D2A, D3A DnA, said second set of main register inputs being DIB, D2B, D3B DnB, said OR gates CIA, C2A, C3A CnA and CIB, C2B, C3B .CnB being connected to corresponding respective main register inputs DIA, D2A, D3A DnA and DIB, D28, D38 DnB, said reset means having a first set of output devices BIA, 82A, 83A BnA, said reset means also having a second set of output devices BIB, B2B, B3B BnB, said OR gates CIA, C2A, C3A CnA and CIB, C2B, C3B CnB having first inputs CIAI, C2AI, C3AI CnAl and CIBI, C2Bl, C3BI CnBI, respectively, said OR gates CIA, C2A, C3A .CnA and CIB, C2B, C3B CnB also having second inputs ClA2, C2A2, C3A2 CnA2 and CIB2, C282, C382 CnB2, respectively, said output devices BIA, 82A, 83A BnA connected to said first inputs CIAI, C2AI, C3A1 CnAI, respectively, said logic circuit having corresponding respective different outputs connected to said OR gate second inputs. 

1. A digital control system comprising: densitometer apparatus for producing output pulses at a pulse repetition frequency f approximately proportional to the density d of a fluid such that d -RF + S where R and S are constants; a main storage register; reset means to enter a predetermined number into said main register periodically, said predetermined number being equal to V, where V STTo/R To is the time width of a pulse pg, and T is a constant; a gate; synchronization means, logic means connected to and from said main register and from said gate to cause the count stored in said main register to be reduced by one upon receipt thereby of each output pulse of said gate; an output storage register; a gating circuit connected from said synchronization means and said main storage register to said output storage register, said gate being connected from said densitometer apparatus, said synchronization means being constructed to impress pulses pg on said gate to cause said gate to pass densitometer apparatus pulses to said logic means at a rate equal to Tf, said synchronization means holding said gate open periodically for periods large in comparison to the reciprocal of Tf, said synchronization means impressing a pulse pr periodically on said reset means to cause reset means to enter said predetermined number in said main register at a time which precedes the first output pulse of said gate after it is opened, said synchronization means being connected to said gating circuit to supply a pulse pc thereto to cause the number stored in said main register to be transferred into said output storage register after said gate is closed; and utilization means connected from said output storage register.
 2. The invention as defined in claim 1, wherein said synchronization means generates said pulses pg, pr and pc in synchronism.
 3. The invention as defined in claim 2, wherein said pulses pg, pr and pc have pulse repetition frequencies fg, fr and fc, respectively, where fg fr fc, all of said pulses, pg, pr and pc occurring during mutually exclusive intervals of time, each pulse immediately succeeding a pulse pr being a pulse pg, each pulse immediately succeeding a pulse pg being a pulse pc.
 4. The invention as defined in claim 3, wherein the pulse width of each of said pulses pg is invariant with time.
 5. The invention as defined in claim 4, wherein said predetermined number is invariant with time.
 6. The invention as defined in claim 5, wherein said reset means is manually adjustable to change said predetermined number.
 7. The invention as defined in claim 6, wherein first and second sets of OR gates are provided, said first set of OR gates including OR gates C1A, C2A, C3A . . . CnA, said second set of OR gates including OR gates C1B, C2B, C3B . . . CnB, said main storage register having first and second sets of inputs, said first set of main register inputs being D1A, D2A, D3A . . . DnA, said second set of main register inputs being D1B, D2B, D3B . . . DnB, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB being connected to corresponding respective main register inputs D1A, D2A, D3A . . . DnA and D1B, D2B, D3B . . . DnB, said reset means having a first set of output devices B1A, B2A, B3A . . . BnA, said reset means also having a second set of output devices B1B, B2B, B3B . . . BnB, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB having first inputs C1A1, C2A1, C3A1 . . . CnA1 and C1B1, C2B1, C3B1 . . . CnB1, respectively, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB also having second inputs C1A2, C2A2, C3A2 . . . CnA2 and C1B2, C2B2, C3B2 . . . CnB2, respectively, said output devices B1A, B2A, B3A . . . BnA being connected to said first inputs C1A1, C2A1, C3A1 . . . CnA1, respectively, said logic circuit having corresponding respective different outputs connected to said OR gate second inputs.
 8. The invention as defined in claim 7, wherein said utilization means includes means to indicate the magnitude of the number stored in said storage register.
 9. The invention as defined in claim 2, wherein said first and second sets of OR gates are provided, said first set of OR gates including OR gates C1A, C2A, C3A . . . CnA, said second set of OR gates including OR gates C1B, C2B, C3B . . . CnB, said main storage register having first and second sets of inputs, said first set of main register inputs being D1A, D2A, D3A . . . DnA, said second set of main register inputs being D1B, D2B, D3B . . . DnB, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB being connected to corresponding respective main register inputs D1A, D2A, D3A . . . DnA and D1B, D2B, D3B . . . DnB, said reset means having a first set of output devices B1A, B2A, B3A . . . BnA, said reset means also having a second set of output devices B1B, B2B, B3B . . . BnB, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB having first inputs C1A1, C2A1, C3A1 . . . CnA1 and C1B1, C2B1, C3B1 . . . CnB1, respectively, said OR gates C1A C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB also having second inputs C1A2, C2A2, C3A2 . . . CnA2 and C1B2, C2B2, C3B2 . . . CnB2, respectively, said output devices B1A, B2A, B3A . . . BnA being connected to said first inputs C1A1, C2A1, C3A1 . . . CnA1, respectively, said logic circuit having corresponding respective different outputs connected to said OR gate second inputs.
 10. The invention as defined in claim 3, wheein first and second sets of OR gates are provided, said first set of OR gates including OR gates C1A, C2A, C3A . . . CnA, said second set of OR gates including OR gates C1B, C2B, C3B . . . CnB, said main storage register having first and second sets of inputs, said first set of main register inputs being D1A, D2A, D3A . . . DnA, said second set of main register inputs being D1B, D2B, D3B . . . DnB, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB being connected to corresponding respective main register inputs D1A, D2A, D3A . . . DnA and D1B, D2B, D3B . . . DnB, said reset means having a first set of output devices B1A, B2A, B3A . . . BnA, said reset means also having a second set of output devices B1B, B2B, B3B . . . BnB, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB having first inputs C1A1, C2A1, C3A1 . . . CnA1 and C1B1, C2B1, C3B1 . . . CnB1, respectively, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB also having second inputs C1A2, C2A2, C3A2 . . . CnA2 and C1B2, C2B2, C3B2 . . . CnB2, respectively, said output devices B1A, B2A, B3A . . . BnA being connected to said first inputs C1A1, C2A1, C3A1 . . . CnA1, respectively, said logic circuit having corresponding respective different outputs connected to said OR gate second inputs.
 11. The invention as defined in claim 4, wherein first and second sets of OR gates are provided, said first set of OR gates including OR gates C1A, C2A, C3A . . . CnA, said second set of OR gates including OR gates C1B, C2B, C3B . . . CnB, said main storage register having first and second sets of inputs, said first set of main register inputs being D1A, D2A, D3A . . . DnA, said second set of main register inputs being D1B, D2B, D3B . . . DnB, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB being conneCted to corresponding respective main register inputs D1A, D2A, D3A . . . DnA and D1B, D2B, D3B . . . DnB, said reset means having a first set of output devices B1A, B2A, B3A . . . BnA, said reset means also having a second set of output devices B1B, B2B, B3B . . . BnB, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB having first inputs C1A1, C2A1, C3A1 . . . CnA1 and C1B1, C2B1, C3B1 . . . CnB1, respectively, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB also having second inputs C1A2, C2A2, C3A2 . . . CnA2 and C1B2, C2B2, C3B2 . . . CnB2, respectively, said output devices B1A, B2A, B3A . . . BnA being connected to said first inputs C1A1, C2A1, C3A1 . . . CnA1, respectively, said logic circuit having corresponding respective different outputs connected to said OR gate second inputs.
 12. The invention as defined in claim 5, wherein first and second sets of OR gates are provided, said first set of OR gates including OR gates C1A, C2A, C3A . . . CnA, said second set of OR gates including OR gates C1B, C2B, C3B . . . CnB, said main storage register having first and second sets of inputs, said first set of main register inputs being D1A, D2A, D3A . . . DnA, said second set of main register inputs being D1B, D2B, D3B . . . DnB, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB being connected to corresponding respective main register inputs D1A, D2A, D3A . . . DnA and D1B, D2B, D3B . . . DnB, said reset means having a first set of output devices B1A, B2A, B3A . . . BnA, said reset means also having a second set of output devices B1B, B2B, B3B . . . BnB, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB having first inputs C1A1, C2A1, C3A1 . . . CnA1 and C1B1, C2B1, C3B1 . . . CnB1, respectively, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB also having second inputs C1A2 C2A2, C3A2 . . . CnA2 and C1B2, C2B2, C3B2 . . . CnB2, respectively, said output devices B1A, B2A, B3A . . . BnA being connected to said first inputs C1A1, C2A1, C3A1 . . . CnA1, respectively, said logic circuit having corresponding respective different outputs connected to said OR gate second inputs.
 13. The invention as defined in claim 1, wherein first and second sets of OR gates are provided, said first set of OR gates including OR gates C1A, C2A, C3A . . . CnA, said second set of OR gates including OR gates C1B, C2B, C3B . . . CnB, said main storage register having first and second sets of inputs, said first set of main register inputs being D1A, D2A, D3A . . . DnA, said second set of main register inputs being D1B, D2B, D3B . . . DnB, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB being connected to corresponding respective main register inputs D1A, D2A, D3A . . . DnA and D1B, D2B, D3B . . . DnB, said reset means having a first set of output devices B1A, B2A, B3A . . . BnA, said reset means also having a second set of output devices B1B, B2B, B3B . . . BnB, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB having first inputs C1A1, C2A1, C3A1 . . . CnA1 and C1B1, C2B1, C3B1 . . . CnB1, respectively, said OR gates C1A, C2A, C3A . . . CnA and C1B, C2B, C3B . . . CnB also having second inputs C1A2, C2A2, C3A2 . . . CnA2 and C1B2, C2B2, C3B2 . . . CnB2, respectively, said output devices B1A, B2A, B3A . . . BnA connected to said first inputs C1A1, C2A1, C3A1 . . . CnA1, respectively, said logic circuit having corresponding respective different outputs connected to said OR gate second inputs. 